Yes but I have a feeling it's probably not going to give you what you want.

You'll still have to have different subnets. For example if the network your client mode WRT is connected to uses the 192.168.1.x range you MUST configure something different such as 192.168.2.x for the LAN side of the WRT in client mode.

To get all the clients on the same subnet you need something being called Bridged Client Mode, currently only available in Talisman. (I believe BrainSlayer is planning on adding it to DD-WRT but it is not yet in the v22Prefinal5 release...)